With the addition of Oscar-winning A-lister Catherine Zeta-Jones to a cast that already includes George Clooney, Julia Roberts and Brad Pitt, the marquee for the sequel to “Ocean’s Eleven” is looking very crowded indeed.

A combination of any two of these stars would be enough for “Ocean’s Twelve” – Steven Soderbergh’s follow-up to his ring-a-ding-ding Rat Pack remake of 2001 – to be deemed star-studded.

“If you can have [one of] the most beautiful woman [Roberts] in the world, why not get the other one?” he asked The Post. Zeta-Jones and Roberts starred together in 2001’s “America’s Sweethearts.”

“And then if you can get some of the greatest hunks in the world on one screen in one movie, why not?”

Tinseltown was abuzz yesterday at the idea of clashing egos, sky-high budgets and celebrity catfights over top billing.

But Weintraub insists none of that will be a problem.

“They’re all great friends. They can’t wait to start shooting [in April],” he said.

“This is not hard duty. We’re shooting it in Europe. We’re going to have a lot of fun, and the movie’s going to sell a lot of popcorn.”

Clooney will reprise his pivotal role as veteran thief Danny Ocean, who led a gang of associates in the heist of three Las Vegas casinos in the hit 2001 film – and will head an international looting spree in “Twelve.”

Zeta-Jones will play a beautiful Europol agent named Isabel Lahiri who specializes in tracking down master thieves and who was once in a serious relationship with Pitt’s character, Rusty Ryan.

Soderbergh, who worked with Zeta-Jones on the acclaimed drug drama “Traffic,” and Clooney, who starred opposite her in the recent Coen brothers’ comedy “Intolerable Cruelty,” were both keen to have her join the cast.

For Zeta-Jones – who just dumped her agent reportedly because she wasn’t getting the roles Nicole Kidman was being offered – “Twelve” may be an opportunity to ditch her diva reputation.

“Besides being part of a hit, this is a chance for her to be regular, to show that Clooney and Soderbergh – who doesn’t put up with a lot of cranky actors – want her to be part of the party,” says David Poland, editor of moviecitynews.com.

Filming on “Twelve” is sure to be a party, with shooting in Paris, Rome, Amsterdam and Monte Carlo.

This uncommon aligning of the stars harks back to the Golden Age of cinema, when studios had big-name celebrities under contract and could shoehorn as many as they pleased into one movie.

MGM, for example, had so many A-listers on board, they could stuff 1940’s “The Philadelphia Story” with the top-flight cast of Katharine Hepburn, James Stewart and that Clooney prototype, Cary Grant.

Operating independently, Tinseltown’s finest actors now demand up to $25 million a picture, which can bloat a movie’s budget beyond feasibility when even more than one comes aboard.

Soderbergh has said he’s aiming to make “Ocean’s Twelve” a “bigger movie” using the same size budget he had for “Ocean’s Eleven,” $85 million.

Naturally, that means asking his stars to take an even bigger pay cut than they did for the first film – and, with the addition of Zeta-Jones, the cash will be spread even thinner.

But most stars would be happy to do it for Soderbergh.

“Right now in Hollywood, there are a limited number of good directors,” says Horak.

“The directors who are both commercially viable and artistically ambitious are few, and Soderbergh is one of them.”

At 41, the arty, baseball cap-wearing auteur has gathered around him an informal repertory company – which just happens to include some of the biggest names in Hollywood, like his pal and producing partner Clooney.

Yet Soderbergh tends to use the actors in his unofficial stable for specific, quite small roles rather than casting them for star value.

Roberts, for example, was happy to work as an undistinguished member of an ensemble cast in Soderbergh’s experimental “Full Frontal,” in which Pitt put in a brief cameo as himself.

“They all seem to like each other. They’ve made choices to work together which were not just business decisions,” says Poland.

“[Ocean’s Twelve”] is going to sell itself, so theoretically they didn’t need Zeta-Jones to put it over at all. She’s obviously also part of the family now.”

But don’t expect an outbreak of sibling rivalry from any of the cast, including Zeta-Jones, says Horak.

“At this point, some of these actors – Zeta-Jones particularly – probably have more money than they’ll ever need and may be willing to do things just for the fun of it.”